The proposed project will investigate the effect of altering membrane fluidity and lipid phase transition temperatures on the function of biological membranes. Membrane lipids, which are critical in the maintenance of ion gradients, signal transduction, and modulation of the activity of integral membrane proteins, are easily perturbed by environmental conditions such as exposure to chemicals and drugs, and temperature changes. Models of membrane regulation have focused on either membrane fluidity or lipid phase state as the critical biophysical properties that must be regulated in order to preserve function. This project will use dietary manipulations in Drosophila melanogaster to vary membrane lipid characteristics and thus to change membrane fluidity and phase transition temperatures independently. The effects of fluidity and transition temperature changes will be tested by exposing the flies to different temperatures and assessing the performance of the membranes and survival of larvae. Simultaneous characterization of membrane composition and biophysical properties in Drosophila under a variety of conditions will establish more clearly the link between membrane composition and membrane biophysical properties. This project will develop Drosophila as a model for membrane studies in animal systems.